Samantha rose early Saturday morning. She chased a pair of chinchillas out of her room, then took a quick shower and got dressed. She grabbed her umbrella and put the sunglasses in her purse. On the way down to the kitchen, she passed Dennis, who was chasing a chinchilla headed up to the second floor. She was only half awake, so the sound of rodents squeaking and plastic cone clattering was extra-irritating. She and Nipper had a new clue, though, a good one, and they were about to check it out. That improved her mood.

She made breakfast while she waited for her brother. She filled a bowl with cereal and went to the refrigerator for milk. Before she could sit down, a chinchilla dashed across the table and scampered away with her spoon in its mouth.

Samantha watched the rodent retreat to a far corner of the kitchen. It looked up at her and opened its tiny mouth, letting the spoon drop on the floor. It began to squeak at her repeatedly.

Samantha thought it sounded like the chinchilla was laughing at her.

“You know what animals I really love?” she said to the chinchilla. “Owls, skunks, and foxes.”

“Really? Since when?” Nipper said cheerfully, walking into the room.

Before she could respond, he grabbed a bowl and two spoons. He handed one of the spoons to his sister and they both dug in, eating quickly.

“I’ve got my hand lens,” said Nipper, waving his magnifying glass at Samantha.

She nodded, then grabbed her purse and umbrella, and they headed out the front door.

“Sam, did you know that owls, skunks, and foxes are natural predators of chinchillas?” Nipper asked as they headed north on Thirteenth Avenue.

“Yes,” she replied. “An eight-year-old boy told me that several times this week.”

Nipper tilted his head sideways and stared off into space. She could tell he was replaying events of the week in his mind.

“That was me, Sam, wasn’t it?” he finally said.

Samantha noticed Missy Snoddgrass watching them through the bay window of her house. She wore the same yellow polka-dot blouse as always and pounded one fist rhythmically onto her open palm as she watched them walk by.

Samantha quickly took the purple sunglasses and put them on Nipper’s face.

“Huh?” he asked. “What are you—”

“You should try these first today,” she said.

Samantha was determined to get to the park before her brother paid another punishing visit to their neighbor’s house. He always came back in a bad mood.

“Keep a watch out for any lights or clues,” she said.

“I’m on it,” said Nipper.

He began to stare straight ahead toward the end of the block.

“Distraction prevented,” Samantha said quietly to herself.

They passed the Snoddgrass lair and reached the mailbox. She pictured the arrow beneath it pointing across the street into Volunteer Park.

“Follow me and keep looking,” she said, and led Nipper across the street.

They walked around the water tower and crossed to the front of the art museum.

“Take your time,” she told him. “Make sure you don’t miss anything.”

Nipper stood with his hands at his sides and began to turn around slowly.

“Beep…beep…beep,” he said, imitating radar or some kind of warning device.

“How is it possible,” she asked, “that you can be annoying in any situation?”

“Beep…beep…oh, I don’t know, Sam,” he replied. “It just comes natural to me. Beep.”

“Stop it,” she said. “Right now. No more noises.”

He stared at her. His lips moved, but he stopped making beeping sounds out loud.

Samantha waited as Nipper went back to staring and turning. Slowly and silently, he spun all the way around. He looked at the art museum, south toward their house, west over Downtown and to the Olympic Mountains beyond. He finished his 360-degrees rotation, then stared at her.

“Anything?” she asked.

He pointed to his mouth. His lips were closed tight.

“Speak,” she said.

“Bee-eep…prepared to keep walking,” he said. “There’s nothing secret here.”

Samantha groaned.

“You are exceptionally annoying,” she said. “Let’s move on.”

They walked past the museum and farther north into the park. The sidewalk curved around a field dotted with picnic tables. It continued to the Volunteer Park Conservatory, a two-story, glass-and-iron greenhouse.

“Beep,” said Nipper.

“Again?” Samantha asked, irritated. “When you make those sounds you are super-annoy—”

“Listen, Sam,” he insisted. “Bee-beep-beep. I see—beep. Something yellow—beep. In front of the—beep. Conservatory and—”

She snatched the glasses from her brother’s face and followed his gaze. To the right of the walkway, a few feet from the glass doors to the greenhouse, a red fire hydrant stood in the grass.

She put the glasses on. The hydrant glowed yellow. Toward the top, extra-bright yellow letters flashed:

PSST

She stared at the hydrant. It was waist high and had a domed cap. A large round outlet on its front faced her. Two smaller outlets stuck out on either side like stubby arms. Short chains connected the pentagon-shaped bolts to the body of the hydrant.

While Samantha put the glasses in her purse, Nipper pushed past her.

“I’ve got this,” he said as he reached the hydrant.

First, he put his hands on the domed cap and tried to twist it. Then he tugged at the chains. Finally, he pulled on the two arms and tried to get the whole hydrant to turn.

“I can do it, Sam,” he grunted, putting his full weight into it. “I’m sure there’s…a way…to make it…”

Nipper lost his grip and his footing, falling onto the grass behind the hydrant.

“Ouch!” he said, looking up at Samantha. “I just fell on my hand lens.”

“Get up and pass it to me,” she replied. “I want to check the Plans.”

Samantha unslung the umbrella from her shoulder, raised it above her head, and popped it open. Then she extended a hand to Nipper, who was still lying on the ground. As she waited for the magnifier, she looked past her fingertips at the hydrant. The large bolt on top of the cap caught her attention. She quickly turned and looked at the open umbrella. Then she looked down at the bolt again. Each had eight sides. They were both octagons! It couldn’t be a coincidence.

Samantha stepped off the path toward the hydrant. Meanwhile, Nipper was running his fingers through the grass.

“Hey, this is fake,” he said. “It’s artificial turf.”

Samantha focused on the octagonal bolt. She reached out, grabbed it, and gave it a quick turn. Immediately, she heard a soft click and a loud hiss. The ground shook. She reached out again to steady herself. The lawn surrounding the hydrant, about three feet in all directions, began to drop slowly. They were sinking into the park on a green, ring-shaped platform.

“Interesting,” said Nipper, standing up quickly.

Samantha watched the fire hydrant rise above them in the center of the ring as they descended. They dropped below street level and continued downward until, with a gentle bump, they came to a stop. Looking up, she saw the fire hydrant thirty feet above, framed by the sky. Some light trickled down, but not much. Machinery droned softly, and she heard what sounded like sheets of sandpaper rubbing together.

Something clicked and lights came on.

They stood in the center of a small room It was about ten feet to the wall all around. The floor beyond the edge of the platform was rotating clockwise.

The white tile walls surrounding them had four wide rectangular openings, spaced evenly around the chamber. Samantha read a large sign above each one.

NORWAY

4,500 MILES

PERU

5,000 MILES

MALI

6,500 MILES

INDONESIA

8,300 MILES

In the past few months, Samantha and Nipper had done so much traveling on mysterious, barely labeled trains, tubes, and ladders, it felt strange to be in a place with such clear signage.

Painted on the walls between the openings, Samantha saw:

SLIDEWALK

KEEP RIGHT

“Ever hear of a ‘slidewalk’?” she asked.

Nipper shook his head.

They stepped onto the rotating floor.

“ ‘Slidewalk…slidewalk…slidewalk,’ ” she read, watching the walls go by. “I have a feeling we’re about to find out.”

As they began their second orbit around the room, they peeked through the entrances and saw that each had two conveyor belts. The one on the right led away. The one on the left led back to the chamber.

“Okay, Sam,” said Nipper. “Where to?”

Samantha started to reach for the umbrella on her shoulder, but then stopped. She scanned the signs above each opening again. Then she smiled.

“A-L-I-M,” she replied. “Unscrambled, that’s…”

She waited for her brother to answer.

He stared at her blankly.

“I-L-A-M backward is…,” she tried again.

“Mali,” he said.

“It’s in Africa,” she told him.

“Oh, yeah. Of course,” he said. “It’s one of the sixteen landlocked African countries.”

As they stepped through the entrance, Samantha marveled at her brother’s capacity for useless facts.